We propose to study the properties, mechanism of action and biological significance the oxygen-dependent antimicrobial systems of phagocytes. Phagocytes respond to perturbation of the plasma membrane with a burst of oxygen consumption and extra oxygen consumed is converted to the superoxide anion, hydrogen peroxide, hydroxyl radicals and possible singlet oxygen, each of which may contribute to themicrobicidal activity of the cells. the toxicity of H2O2 is increased considerably by the addition of peroxidase and a halide and this antimicrobial system appears to play a role in certain phagocytes (e.g. neutrophils, monocytes). Our aim is to determine the mechanism of target cell destruction by these antimicrobial systems with emphasis on the oxidation of iron centers with the release of iron into the medium. Intact organisms, membrane vesicles or model iron-containing compounds will be exposed to isolated antimicrobial systems and, in some instances, to intact phagocytes. The organisms will be prelabeled with 59Fe, and polyacrylamide gel electrophoresis, radioautography and histochemical staining will be employed to identify the proteins primarily affected. The binding of the released iron by lactoferrin will be investigated since this iron-binding protein is present in neutrophil granules and may serve as a biological chelator of the iron in situ. The properties of a new iron-containing antimicrobial system consisting of iron, H2O2 and iodide will be investigated with emphasis on the usefulness of this system for the disinfection of water of organisms which induce diarrhea (e.g. Giardia cysts). A study of the susceptibility of the intracellular pathogen Mycobacterium leprae to the antimicrobial systems of phagocytes will be undertaken in an attempt to determine the basis for their host resistance. A microscopic and metabolic method for the rapid detection of viability of M leprae will be evaluated. Neutrophil function of selected patients with an increased susceptibility to infectionwill be evaluated in an attempt to elucidate the basis for the dysfunction. The long term goals are 1) to determine the role of these systems in the killing of microorganisms by phagocytes; 2) to determine whether alterations in these systems contribute to the pathogenesis of disease; and 3) to determine whether manipulations of these systems influence the course of disease.